bug#8222: 24.0.50; problem with themeing var with repeat string

[Chong Yidong]

joakim@verona.se writes:

> - programmatically enabling a theme when there is another custom enabled
> theme already.
>
> Ill open a new bug for the second case which is also more important.

I didn't see you file a new bug for this, but I've now committed a fix
for this problem too.  Could you test the code in trunk and see if it
works for you?  Thanks.